JP6999259B2 - Plain bearing - Google Patents

Description

The present invention relates to a sliding bearing that slides through a mating material to be supported and a lubricating film.

Sintered oil-impregnated bearings, which are a type of slide bearings, may be used for rotary support bearings of small motors such as spindle motors for HDDs, polygon scanner motors for laser beam printers, and fan motors for cooling fans. .. Sintered oil-impregnated bearings are impregnated with oil (or grease; the same applies hereinafter) in the internal pores, and this oil seeps out from the bearing surface to supply oil to the sliding part between the bearing surface and the shaft. Lubricity can be improved.

However, when the pressure of the oil film in the bearing gap increases, a part of the oil escapes from the opening of the bearing surface of the sintered oil-impregnated bearing to the outside through the internal pores, so that the pressure of the oil film decreases and the load capacity increases. It will drop. In order to suppress such pressure release from the opening of the bearing surface, for example, in Patent Document 1 below, a mold (for example, a mandrel) is slid on the bearing surface to seal the opening of the bearing surface. The technology to do is shown.

Japanese Patent No. 3377681

However, if the mold is slid to seal the bearing surface as described above, the bearing surface is easily scratched and the quality may deteriorate. In addition, the number of processes and dies for sealing the bearing surface is increased, which increases the cost.

In addition to the above, as a means for suppressing pressure release from the opening of the bearing surface, for example, the volume of internal pores can be reduced by increasing the molding pressure of the green compact to increase the density, or molten resin or molten metal. There is a method of infiltrating and filling the internal pores. However, increasing the density by increasing the forming pressure of the green compact has limitations in terms of the capacity of the press machine, the strength of the die, and the productivity. Further, the sealing with the molten resin or the molten metal makes it difficult to maintain the accuracy of the bearing surface, and also requires a large amount of man-hours to increase the cost.

Further, if the opening of the bearing surface is completely sealed or the bearing surface is made smooth by forming a slide bearing with a material having no pores such as molten steel, the decrease in oil film pressure can be prevented. However, in this case, since the oil is not supplied from the internal pores, the oil on the sliding portion between the bearing surface and the shaft is likely to be depleted, and seizure may occur due to the contact between the bearing surface and the shaft.

Therefore, the present invention suppresses pressure release from the bearing surface to increase the load capacity without increasing the cost, and prevents the lubricating film from breaking at the sliding portion between the bearing surface and the mating material (shaft). The purpose is to prevent seizure.

In order to solve the above-mentioned problems, the present invention is composed of a green compact in which the particles are bonded to each other by an oxide film formed on the surface of the particles of the metal powder, via a mating material to be supported and a lubricating film. A slide bearing having a sliding bearing surface is characterized in that the bearing surface has a large number of openings in which communication with internal pores is blocked by the oxide film.

In the sliding bearing of the present invention, the green compact is not sintered at a high temperature (for example, 850 ° C.) as in a general sintered bearing, but the green compact is heat-treated at a relatively low temperature (for example, 500 ° C.). An oxide film is formed on the surface of the particles of the metal powder constituting the green compact, and the particles are bonded to each other by the oxide film. In this case, the oxide film fills at least a part of the internal pores of the green compact, which makes it difficult for oil to escape from the surface of the green compact to the inside. Therefore, the bearing does not need to be separately sealed. It is possible to suppress the pressure release from the surface and increase the load capacity.

Further, the above oxide film does not completely seal the openings on the surface of the green compact to make the bearing surface smooth, and the oxide film on the surface of the green compact has internal pores. Numerous openings remain where communication is blocked. This opening functions as an oil reservoir for holding oil, and the oil held in the opening is supplied to the sliding portion between the bearing surface and the mating material, so that the oil film can be prevented from running out in the sliding portion. .. The "internal pores" mean pores formed by particles not exposed on the surface of the green compact or an oxide film formed on the surface thereof.

The above-mentioned slide bearing preferably has an oil content of 4 vol% or less and a surface opening ratio of the bearing surface of 40% or more. The surface aperture ratio is the area ratio of all the openings on the bearing surface, including not only the openings not communicating with the internal pores as described above but also the openings communicating with the internal pores.

Further, the above-mentioned slide bearing preferably has an oil permeability of 0.01 g / 10 min or less. The degree of oil flow is determined by contacting the surface of the plain bearing (for example, the inner peripheral surface) with oil and holding the oil under a predetermined pressure (0.4 MPa in this case) for 10 minutes. It is determined by measuring the total weight of the oil exuded from the opening on the opposite surface (eg, the outer peripheral surface).

The bearing surface can be, for example, a smooth cylindrical surface having no dynamic groove or the like. This plain bearing can form a fluid dynamic bearing by facing the outer peripheral surface of the shaft member on which the dynamic pressure groove is formed, or can form a perfect circular bearing by facing the cylindrical outer peripheral surface of the shaft member. be able to.

Further, a dynamic pressure groove may be formed on the bearing surface. This plain bearing can form, for example, a fluid dynamic bearing so as to face the smooth outer peripheral surface or end surface of the shaft member.

The above-mentioned plain bearing can be incorporated into, for example, a fluid dynamic bearing device. Specifically, the above-mentioned slide bearing and the shaft member as the mating material inserted in the inner circumference of the slide bearing are provided, and a radial surface between the bearing surface of the slide bearing and the outer peripheral surface of the shaft member is provided. It is possible to obtain a hydrodynamic bearing device that non-contactly supports the shaft member in a relative rotatable manner by the pressure of the lubricating film in the bearing gap.

As described above, in the present invention, by filling at least a part of the internal pores of the slide bearing (compact powder) with the oxide film, it is possible to suppress the pressure release from the bearing surface and increase the load capacity. Further, by providing a large number of openings for oil pools on the bearing surface of the slide bearing, it is possible to prevent the oil film from running out at the sliding portion with the mating material and prevent seizure.

It is sectional drawing of a spindle motor. It is sectional drawing of the fluid dynamic pressure bearing apparatus. It is sectional drawing of the slide bearing (bearing sleeve) which concerns on one Embodiment of this invention. It is a bottom view of the above-mentioned plain bearing. It is sectional drawing in the vicinity of the bearing surface of the above-mentioned plain bearing. It is a photograph of the bearing surface of the above-mentioned plain bearing. It is sectional drawing (before molding) of the forming die which performs a compaction process. It is sectional drawing of the forming die which performs a compaction process (at the time of completion of molding). It is sectional drawing of the forming die which performs a compaction process (at the time of mold release). The left figure is a cross-sectional structure chart of the green compact before the heat treatment, the central figure is a cross-sectional structure chart of the green compact after degreasing, and the right figure is a cross-sectional structure chart of the green compact after the oxidation treatment. It is a graph which shows the relationship between the true density ratio of a green compact and an oil content. It is a graph which shows the rotation speed and the oil film formation rate of the motor which has a slide bearing which concerns on an Example. It is a graph which shows the rotation speed and the oil film formation rate of the motor which has a slide bearing which concerns on a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The spindle motor shown in FIG. 1 is used for a disk drive device such as an HDD, and is a fluid dynamic bearing device 1 that rotatably and non-contactly supports the shaft member 2 and a disc hub 3 mounted on the shaft member 2. And, for example, a stator coil 4 and a rotor magnet 5 which are opposed to each other via a gap in the radial direction are provided. The stator coil 4 is attached to the casing 6, and the rotor magnet 5 is attached to the disc hub 3. The housing 7 of the fluid dynamic bearing device 1 is mounted on the inner circumference of the casing 6. A predetermined number of discs D such as magnetic disks are held in the disc hub 3. When the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the disc hub 3 and the shaft member 2 are rotated together.

As shown in FIG. 2, the hydrodynamic bearing device 1 includes a bearing sleeve 8 as a slide bearing according to an embodiment of the present invention, a shaft member 2 as a mating material supported by the bearing sleeve 8, and a bearing sleeve. It has a housing 7 that holds 8 on the inner circumference, a seal portion 9 provided at an opening at one end in the axial direction of the housing 7, and a thrust bush 10 that closes the other end in the axial direction of the housing 7. In the illustrated example, the housing 7 and the seal portion 9 are composed of one component. In the following description, for convenience, the closed side of the housing 7 is referred to as the lower side and the opening side of the housing 7 is referred to as the upper side in the axial direction, but this does not mean that the usage mode of the fluid dynamic bearing device 1 is limited.

The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided at the lower end of the shaft portion 2a. The shaft member 2 is formed of, for example, metal, and in the present embodiment, the entire shaft member 2 including the shaft portion 2a and the flange portion 2b is integrally formed of stainless steel.

The housing 7 is made of resin or metal and is formed in a cylindrical shape. The outer peripheral surface 8d of the bearing sleeve 8 is fixed to the inner peripheral surface 7a of the housing 7 by an appropriate means such as adhesion or press fitting.

The bearing sleeve 8 has a cylindrical shape, and a radial bearing surface facing the outer peripheral surface 2a1 of the shaft member 2 is provided on the inner peripheral surface 8a. In the illustrated example, radial bearing surfaces A are formed at two locations separated in the axial direction from the inner peripheral surface 8a of the bearing sleeve 8. Dynamic pressure grooves are formed on each radial bearing surface A, and in the present embodiment, as shown in FIG. 3, dynamic pressure grooves G1 and G2 arranged in a herringbone shape are provided on each radial bearing surface A. The area shown by cross-hatching in the figure indicates a hill portion that rises toward the inner diameter side (the same applies to FIG. 4).

The upper dynamic pressure groove G1 has an asymmetrical shape in the axial direction, and the lower dynamic pressure groove G2 has a symmetrical shape in the axial direction. The oil in the radial bearing gap is pushed in the axial direction by the upper dynamic pressure groove G1 having an axially asymmetrical shape, and the oil is forcibly circulated inside the housing 7. A cylindrical surface continuous with the bottom surfaces of the dynamic pressure grooves G1 and G2 is provided in the axially interaxial region of the radial bearing surface A. Both the upper and lower dynamic pressure grooves G1 and G2 may have axially symmetrical shapes. Further, the upper and lower dynamic pressure grooves G1 and G2 may be made continuous in the axial direction, or one or both of the upper and lower dynamic pressure grooves G1 and G2 may be omitted. Further, a spiral-shaped dynamic pressure groove or a dynamic pressure groove extending in the axial direction may be formed on the radial bearing surface. Further, the inner peripheral surface 8a (radial bearing surface A) of the bearing sleeve 8 may be used as a cylindrical surface, and a dynamic pressure groove may be formed on the outer peripheral surface 2a1 of the shaft member 2.

The lower end surface 8b of the bearing sleeve 8 is provided with a thrust bearing surface B facing the upper end surface 2b1 of the flange portion 2b of the shaft member 2. A pump-in type spiral-shaped dynamic pressure groove G3 as shown in FIG. 4 is formed on the thrust bearing surface B. As the shape of the dynamic pressure groove, a herringbone shape, a radial groove shape, or the like may be adopted. Further, the lower end surface 8b (thrust bearing surface B) of the bearing sleeve 8 may be used as a flat surface, and a dynamic pressure groove may be formed in the upper end surface 2b1 of the flange portion 2b of the shaft member 2.

As shown in FIG. 3, an annular groove 8c1 and a plurality of radial grooves 8c2 provided on the inner diameter side of the annular groove 8c1 are formed on the upper end surface 8c of the bearing sleeve 8. A plurality of axial grooves 8d1 are provided on the outer peripheral surface 8d of the bearing sleeve 8 at equal intervals in the circumferential direction. The space on the outer diameter side of the flange portion 2b of the shaft member 2 communicates with the seal space S through the axial groove 8d1, the annular groove 8c1, the radial groove 8c2, etc., so that the negative pressure in this space can be reduced. Occurrence is prevented. If there is no particular need, the annular groove 8c1 and the radial groove 8c2 may be omitted, and the upper end surface 8c of the bearing sleeve 8 may be a flat surface.

The bearing sleeve 8 is a porous oil-impregnated bearing in which the internal pores of a green compact of metal powder are impregnated with oil. The entire surface of the bearing sleeve 8 is a molded surface including the bottom surfaces of the dynamic pressure grooves G1, G2, and G3, and the top and side surfaces of the hill. The bearing sleeve 8 is not sized and no sliding marks are formed on the surface of the bearing sleeve 8.

The bearing sleeve 8 is made of, for example, a green compact containing 95 wt% or more of a single metal. In the present embodiment, as shown in FIG. 5, the bearing sleeve 8 is composed of a green compact composed of iron particles 11 and an oxide film 12 formed on the surface of the iron particles 11. The iron particles 11 are bonded to each other by the oxide film 12. Specifically, the oxide coating 12 formed on the surface of each iron particle 11 spreads between the iron particles 11 to form a network, thereby ensuring the strength of the bearing sleeve 8.

In the bearing sleeve 8, at least a part of the gap (internal pores) between the iron particles 11 is filled with the oxide film 12, so that the porosity, particularly the porosity (open pore ratio) communicating with the surface is reduced. There is. As a result, the oil content of the bearing sleeve 8 is set to, for example, 4 vol% or less, preferably 2 vol% or less. The oil permeability of the bearing sleeve 8 is, for example, 0.01 g / 10 min or less.

The surface of the bearing sleeve 8 is not completely sealed and smoothed by the oxide film 12, and a large number of openings are provided in the surface of the bearing sleeve 8, particularly the radial bearing surface A and the thrust bearing surface B. 13a (micro concave portion) is formed. The large number of openings 13a have an oxide film that communicates with the internal pores 13b (pores 13b formed by the iron particles 11 not exposed on the surface of the bearing sleeve 8 or the oxide film 12 formed on the surface thereof). It is blocked by 12. That is, before the oxide film 12 is formed, the internal pores 13b and the opening 13a communicate with each other, but when they are separated by the oxide film 12, any surface (for example, the inner peripheral surface 8a) is formed. ) Only the opening 13a is formed. The inner side of the opening 13a is closed with the oxide film 12. The large number of openings 13a function as an oil reservoir for holding oil. The bearing surfaces A and B of the bearing sleeve 8 are also provided with openings 13c communicating with the internal pores 13b. At least a portion of such an opening 13c communicates with another surface of the bearing sleeve 8 (eg, the outer peripheral surface 8d).

The surface aperture ratios of the radial bearing surface A and the thrust bearing surface B of the bearing sleeve 8 are 40% or more, respectively. The surface aperture ratios of the bearing surfaces A and B are measured by analyzing the captured images of the bearing surfaces A and B. FIG. 6 is an enlarged photograph of the inner peripheral surface 8a (radial bearing surface A) of the bearing sleeve 8, and the region shown in black is the opening 13a or 13c. The surface aperture ratio can be obtained by calculating the ratio of the black regions (openings 13a and 13c) in this image. The straight line shown in FIG. 6 is the boundary between the dynamic pressure groove and the hill.

The seal portion 9 projects from the upper end of the housing 7 toward the inner diameter side. In this embodiment, the seal portion 9 is formed integrally with the housing 7. The inner peripheral surface 9a of the seal portion 9 has a tapered shape whose diameter is gradually reduced downward. A wedge-shaped seal space S whose radial width is gradually narrowed downward is formed between the inner peripheral surface 9a of the seal portion 9 and the outer peripheral surface 2a1 of the shaft portion 2a (see FIG. 2). In addition, while the inner peripheral surface of the seal portion 9 is a cylindrical surface, a tapered surface whose diameter is gradually reduced upward is provided on the outer peripheral surface of the shaft portion 2a, and a wedge-shaped seal space S is formed between them. You may.

The thrust bush 10 is formed of, for example, a metal material (brass or the like) or a resin material, and is fixed to the lower end portion of the inner peripheral surface 7a of the housing 7 by an appropriate means such as press fitting or adhesion. A thrust bearing surface C is formed on the end surface 10a of the thrust bush 10. For example, a pump-in type spiral-shaped dynamic pressure groove is formed on the thrust bearing surface C (not shown). As the shape of the dynamic pressure groove, a herringbone shape, a radial groove shape, or the like may be adopted. Further, the end surface 10a (thrust bearing surface C) of the thrust bush 10 may be used as a flat surface, and a dynamic pressure groove may be formed in the lower end surface 2b2 of the flange portion 2b of the shaft member 2.

Oil (or grease) is injected into the fluid dynamic pressure bearing device 1 having the above configuration. In the present embodiment, the space around the inner circumference of the housing 7 is filled with oil including the internal pores of the bearing sleeve 8, and an oil level is formed in the seal space S.

When the shaft member 2 rotates, the bearing surface provided on the bearing sleeve 8 and the thrust bush 10 and the shaft member 2 slide through the oil film. Specifically, a radial bearing gap is formed between the radial bearing surface A of the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a1 of the shaft portion 2a, and the dynamic pressure grooves G1 and G2 provided on the radial bearing surface A form a radial bearing gap. By increasing the pressure of the oil film in the radial bearing gap, the first radial bearing portion R1 and the second radial bearing portion R2 that non-contactly support the shaft member 2 in the radial direction are configured. At the same time, between the lower end surface 8b (thrust bearing surface B) of the bearing sleeve 8 and the upper end surface 2b1 of the flange portion 2b, and below the end surface 10a (thrust bearing surface C) of the thrust bush 10 and the flange portion 2b. Thrust bearing gaps are formed between the side end surfaces 2b2 and the thrust bearing surfaces B and C, respectively, and the pressure of the oil film in the thrust bearing gaps is increased by the dynamic pressure grooves provided in the thrust bearing surfaces B and C, whereby both thrusts of the shaft member 2 are thrust. A first thrust bearing portion T1 and a second thrust bearing portion T2 that are non-contactly supported in the direction are configured.

At this time, when at least a part of the internal pores of the bearing sleeve 8 is filled with the oxide film 12 and the oil content of the bearing sleeve 8 is 4 vol% or less, the pressure of the oil film in the bearing gap is increased. However, the infiltration of oil from the surface of the bearing sleeve 8 (particularly the radial bearing surface A and the thrust bearing surface B) into the inside is suppressed. As a result, the pressure drop of the oil film in the bearing gap is suppressed, so that the load capacity of the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 can be increased.

Further, a large number of openings 13a are provided on the bearing surfaces A and B of the bearing sleeve 8 (see FIG. 5). The opening 13a is a minute recess whose communication with the internal pores 13b is blocked by the oxide film 12, and serves as an oil reservoir for holding the oil. When the shaft member 2 rotates, the oil held in the opening 13a is supplied to the bearing gap to prevent the oil film from running out in the bearing gap and prevent seizure due to contact between the bearing sleeve 8 and the shaft member 2. be able to.

Here, a method of manufacturing the above-mentioned slide bearing (bearing sleeve 8) will be described. The bearing sleeve 8 is manufactured through a dusting step, a degreasing step, an oxidation step, and an oil-impregnating step. Hereinafter, each step will be described in detail.

(1) Powder compaction process The compaction powder process is a step of supplying a raw material powder to a mold and compression-molding it to obtain a cylindrical compaction powder. The method of the dusting process is not particularly limited, and in addition to uniaxial pressure forming, forming by a multi-axis CNC press or the like can be applied.

The raw material powder mainly contains metal powder such as iron powder and copper powder. The iron powder can be used regardless of the production method, and for example, atomized powder or reduced powder can be used. Copper powder can also be used regardless of the production method, and for example, electrolytic powder, atomized powder, and reduced powder can be used. In addition, it is also possible to use an alloy powder whose main component is iron or copper (for example, a pre-alloyed prealloy powder or a partially diffusion alloyed partial diffusion alloy powder). Further, in order to increase the strength and improve the lubricity, a low melting point metal powder such as Sn or Zn or a carbon-based powder such as graphite or carbon black may be added to the raw material powder.

However, the metal powder contained in the raw material powder preferably contains 95 wt% or more of a single type of metal powder, and more preferably consists of only a single metal powder. This is because if the type of metal is different, the thickness of the oxide film formed on the surface of the particles and the adhesion to the base material are different, so that the dimensional accuracy and the bearing characteristics may not be satisfied. If the dimensional accuracy and bearing characteristics are satisfied, a plurality of types of metal powder may be mixed.

A molding lubricant may be added to the raw material powder in order to ensure the lubrication between the raw material powder and the mold in the subsequent compaction step, or the lubrication between the raw material powders. As the molding lubricant, metal soap, amide wax, or the like can be used. The molding lubricant is mixed with the raw material powder as a powder, or a solution in which the above-mentioned molding lubricant is dispersed in a solvent is sprayed or immersed in a metal powder to volatilize and remove the solvent component. The surface of the metal powder may be coated with a molding lubricant.

In the present embodiment, the raw material powder consists only of pure iron powder (reduced iron powder) and a lubricant for molding. The molding lubricant is contained in an amount of 0.1 to 1 wt%, preferably 0.3 to 0.6 wt% with respect to the pure iron powder.

The dusting step is performed using the forming die shown in FIG. 7. The forming die includes a die 21, a core rod 22, an upper punch 23, and a lower punch 24. Molds 22a and 22b having shapes corresponding to the dynamic pressure grooves G1 and G2 are provided on the outer peripheral surface of the core rod 22. On the upper surface of the lower punch 24, a molding die 24a having a shape corresponding to the dynamic pressure groove G3 is provided. In addition, although not shown, a molding die having a shape corresponding to the axial groove 8d1 is provided on the inner peripheral surface of the die 21, and the annular groove 8c1 and the radial groove 8c2 are formed on the lower surface of the upper punch 23. A molding die having a corresponding shape is provided.

First, as shown in FIG. 7, the cavity partitioned by the die 21, the core rod 22, and the lower punch 24 is filled with the raw material powder M. Next, as shown in FIG. 8, the upper punch 23 is lowered to compress the raw material powder M, and the green compact 8'is formed. At the same time, the dynamic pressure grooves G1 and G2 are formed on the inner peripheral surface of the compaction 8'by the molding dies 22a and 22b of the core rod 22, and the compaction 8'is formed by the molding dies 24a of the lower punch 24. A dynamic pressure groove G3 is formed on the lower end surface.

After that, as shown in FIG. 9, by discharging the green compact 8'from the inner circumference of the die 21, the force applied to the green compact 8'toward the inner diameter is released, and the green compact 8'is springed. Back occurs. As a result, the inner peripheral surface of the green compact 8'is expanded in diameter, and the green compact 8'is released from the molding molds 22a and 22b of the core rod 22.

Generally, the higher the density of a sintered part, the higher the strength. However, as in the present embodiment, when the powder is subjected to an oxidation treatment to increase the strength, if the powder density is too high, an oxidizing gas such as air cannot penetrate into the powder. Since the formation of the oxide film is limited to the very surface layer of the green compact, the strength is improved, but it is not preferable. In view of this point, the powder density is preferably 7.2 g / cm ³ or less (true density ratio 91% or less), preferably 7.0 g / cm ³ or less (true density ratio 89% or less).

On the other hand, if the powder density is too low, there is a concern that chipping or cracking may occur during handling (the ratra value is large), or the distance between particles is too long and an oxide film may not be formed between the particles. In view of this point, the powder density is preferably 5.8 g / cm ³ or more (true density ratio 74% or more), preferably 6.0 g / cm ³ or more (true density ratio 76% or more). In particular, in order to fill the internal pores with an oxide film and reduce the oil content of the powder to 4 vol% or less, the powder density should be 6.3 g / cm ³ or more (true density ratio 80% or more), preferably 6. It is preferable to set it to 7. g / cm ³ or more (true density ratio 85% or more). The powder density is measured by the dimensional measurement method. Further, since the density of the powder compact is almost the same even after the subsequent degreasing step and the oxidation step, the preferable range of the powder compact is the preferable range of the density of the bearing sleeve 8.

(2) Solventing step The degreasing step is a step of heating the green compact to remove (degreas) the molding lubricant contained in the green compact. The degreasing step is performed at a temperature higher than the decomposition temperature of the molding lubricant and lower than the oxidation step described later, and is heated at, for example, 300 to 400 ° C. for 60 to 120 minutes. In the green compact 8'before degreasing, as shown in the left figure of FIG. 10, the molding lubricant 14 is arranged in the gap between the iron particles 11, but by performing the degreasing step, FIG. 10 shows. As shown in the central figure, the molding lubricant 14 disappears, and a green compact 8'consisting only of the iron particles 11 is obtained.

In the conventional manufacturing process of a sintered bearing, the green compact is held at a high temperature in the sintering process, so that the lubricant component contained in the green compact is decomposed and is not contained in the sintered product. However, when the present invention is applied, the lubricant component may remain depending on the density of the green compact, the oxidation treatment temperature, and the holding time. Therefore, it is desirable to take a method of providing a degreasing step for decomposing / removing the lubricant component in advance prior to the oxidation treatment and continuously performing the oxidation treatment in the same atmosphere after the degreasing step. However, it has been confirmed that high strength can be achieved even if the oxidation treatment is performed while containing the molding lubricant without providing the degreasing step. Further, the degreasing step may be carried out using a separate heating device in an atmosphere different from that of the oxidizing step (for example, inert gas, reducing gas, vacuum, etc.).

(3) Oxidation step In the oxidation step, the green compact is heated in an oxidizing atmosphere. As a result, as shown in the right figure of FIG. 10, an oxide film 12 is formed on the surface of each particle 11 of the metal powder (iron powder), and the particles 11 are bonded to each other via the oxide film 12. The strength of the green compact 8'is increased. Specifically, the oxide film formed on the surface of each particle of the metal powder by the oxidation step spreads between the iron particles 11 to form a network, whereby the bond is formed by sintering at a high temperature as in the conventional case. By substituting the force, the green compact 8'is increased in strength. Further, in the present embodiment, not all the particles of the iron powder as the main component are bonded via the oxide film, but some particles are in direct contact with each other and fused without passing through the oxide film. is doing.

The formation of the oxide film 12 fills at least a part of the internal pores of the green compact 8'. At this time, at least a part of the opening on the surface of the green compact 8'is blocked from communicating with the internal pores 13b by the oxide film 12. As a result, a large number of openings 13a whose inner side is closed with the oxide film 12 are formed on the surface of the green compact 8'(see FIG. 5).

The treatment conditions (heating temperature, heating time, heating atmosphere) of the above oxidation treatment are such that the green compact 8'has the strength required for a dynamic pressure bearing, and the oxide coating 12 gives the green compact 8'. 'The oil content is set to 4 vol% or less, and the surface opening ratio is set to 40% or more. Specifically, the heating temperature in the oxidation step of the present embodiment is set to 400 ° C. or higher, preferably 450 ° C. or higher. Further, if the heating temperature is too high, the dimensional change of the green compact becomes large, so the heating temperature is set to 600 ° C. or lower, preferably 550 ° C. or lower. The heating time is appropriately set in the range of 5 minutes to 2 hours, and is, for example, 10 to 20 minutes. The green compact that has undergone the oxidation step has a strength required for a slide bearing, specifically, an annular strength of 120 MPa or more, preferably 150 MPa or more.

The heated atmosphere is an oxidative atmosphere in order to promote positive oxidation. However, since the formation rate of the oxide film is too fast in the water vapor atmosphere, it is preferable to use an oxidizing atmosphere in which the formation rate of the oxide film is slower than that of the water vapor atmosphere. Specifically, it is preferable to heat in the atmosphere of air or oxygen, or an oxidizing gas in which an inert gas such as nitrogen or argon is mixed with the air or oxygen. By performing the oxidation treatment in these oxidizing gases, particularly in an air atmosphere, the oxide film formed on the surface of the green compact can be suppressed, so that the decrease in surface roughness of the green compact can be suppressed. Further, in order to obtain a strength that can withstand use as a slide bearing (for example, an annular strength of 120 MPa or more), it is preferable that the oxygen fraction in the heated atmosphere is 2 vol% or more.

The iron oxide film formed on the surface of the iron powder is a mixed phase of two or more of Fe ₃ O ₄ , Fe ₂ O ₃ , and Fe O. The proportion of these oxide coatings depends on the material and treatment conditions.

The increase in strength by the above oxidation step is a material (iron-based, copper-based, iron-copper-based, iron-based, copper-based, iron-copper-based, which is used in conventional general sintered members and is a mixture of iron, copper, or both of them in various ratios. Or it can be applied to copper-iron-based green compacts. However, it is preferable that the metal powder consists of only one type (for example, iron powder) because the thickness of the oxide film and the adhesion to the particles can be made uniform.

Since the treatment temperature of the above oxidation step is lower than that of the conventional sintering step at a high temperature, the dimensional change of the green compact before and after the treatment is small. Therefore, deterioration of the dimensional accuracy of the green compact, particularly the dimensional accuracy of the dynamic pressure groove (groove depth, etc.) is suppressed, and the required accuracy can be satisfied without sizing. By omitting the sizing step in this way, the bearing manufacturing process can be shortened, the cost can be reduced, and the design of the bearing and the forming die becomes easy.

The above oxidation step can be applied regardless of the shape and size of the green compact. Further, since the surface of the green compact that has been subjected to the oxidation step is covered with an oxide film, the rust preventive effect is high, and in some cases, the rust preventive treatment becomes unnecessary. In addition, since the treatment temperature of the oxidation process is relatively low, additives that denature and decompose at temperatures exceeding this treatment temperature (for example, materials with slidability and lubricity) are added to enhance the functionality of the product. It is also possible to plan.

(4) Oil-impregnating step The oil-impregnating step is a step of impregnating the internal pores of the oxide-treated green compact with lubricating oil. Specifically, by immersing the green compact in oil under a reduced pressure environment and then returning it to atmospheric pressure, the oil enters the internal pores through the opening on the surface of the green compact. As described above, the bearing sleeve 8 according to the present embodiment is completed. The oil-impregnating step may be omitted, and the green compact having no oil impregnated inside may be used as the bearing sleeve 8. In this case, after assembling the fluid dynamic bearing device 1 using the bearing sleeve 8 in the dry state, when the internal space of the fluid dynamic bearing device 1 is filled with oil by vacuum impregnation or the like, the internal pores of the bearing sleeve 8 are formed. Is impregnated with oil.

The embodiment of the present invention is not limited to the above. For example, in the above embodiment, the case where both the radial bearing surface and the thrust bearing surface are provided on the bearing sleeve 8 is shown, but the present invention is not limited to this, and the bearing sleeve 8 has only one of the radial bearing surface and the thrust bearing surface. The present invention may be applied to a sliding bearing. For example, the slide bearing according to the present invention may be applied as the thrust bush 10.

Further, in the above embodiment, the case where the dynamic pressure groove is formed in the bearing sleeve 8 is shown, but the present invention is not limited to this. For example, a perfect circular bearing may be configured by using both the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a1 of the shaft member 2 as cylindrical surfaces. In this case, the swing of the shaft member 2 causes dynamic pressure in the oil film in the bearing gap between the bearing sleeve 8 and the shaft member 2, and this dynamic pressure constitutes a fluid dynamic pressure bearing that floats and supports the shaft. Such a fluid dynamic bearing is applied when supporting a shaft that rotates at a relatively high speed, but is not limited to this, and a mating material that rotates at a relatively low speed or a mating material that swings or moves linearly is used. The slide bearing of the present invention can also be applied as a bearing that slides and supports via a lubricating film.

Further, in the above embodiment, the housing 7 and the seal portion 9 are composed of one component, and the thrust bush 10 is formed as a separate body. However, the present invention is not limited to this, and for example, the housing 7 and the thrust bush 10 are formed as one component. The seal portion 9 may be a separate body. Alternatively, the housing 7, the seal portion 9, and the thrust bush 10 may be separated.

Further, in the above embodiment, the fluid dynamic bearing device having a full-fill structure in which the oil level is formed in only one place (inside the seal space S) is shown, but the partial-fill structure in which the oil level is formed in a plurality of places is shown. The slide bearing according to the present invention may be incorporated in the fluid dynamic pressure bearing device.

Further, in the above embodiment, the case where the sliding bearing (bearing sleeve 8) is fixed and the mating material (shaft member 2) rotates is shown. On the contrary, the mating material is fixed and the sliding bearing is provided. It may be rotated. Further, the slide bearing according to the present invention can be used by being incorporated not only in a spindle motor for a disk drive device such as an HDD, but also in a fan motor for a cooling fan, a polygon scanner motor for a laser beam printer, and the like.

The following tests were conducted to confirm the effect of the present invention.

(1) Relationship between oil content and true density ratio After degreasing and oxidizing a plurality of green compacts having different densities to prepare multiple types of cylindrical test pieces, the oil content of each test piece was measured. .. The test piece (compact powder after oxidation treatment) has the same structure as the slide bearing (bearing sleeve 8) of the above embodiment, and is composed of iron particles and an oxide film formed on the surface thereof. The oil content is measured according to JIS Z 2501: 2000.

FIG. 11 shows the measurement results of the oil content of each test piece. According to this figure, even if the true density ratio is about 80%, the oil content is less than half (for example, 4 vol% or less) with respect to 10 vol%, which is the lower limit of the oil content of a general sintered oil-impregnated bearing. When the true density ratio is 85% or more, the oil content is almost 0 vol% (2 vol% or less). From the above, it was clarified that the oil content can be sufficiently suppressed by subjecting the green compact to degreasing and oxidation treatment.

(2) Oil film formation rate A slide bearing according to an example was produced by subjecting a green compact composed of iron powder and a molding lubricant to a degreasing treatment and an oxidation treatment. The slide bearing of the embodiment has the same configuration as the bearing sleeve 8 (see FIGS. 3 and 4) of the above embodiment, has a ring strength of 150 MPa or more, an oil content of 4 vol% or less, and a surface opening of the bearing surface. The rate is 40% or more. On the other hand, a conventional slide bearing made of a copper-iron-based sintered metal was used as a comparative example. The slide bearing of the comparative example has the same shape as the bearing sleeve 8 of the above embodiment, but the manufacturing method is different from that of the embodiment. Specifically, after forming a cylindrical green compact having no dynamic pressure groove, it is sintered to obtain a sintered body, and the sintered body is sized to form a dynamic pressure groove. After that, the inner peripheral surface of the sintered body was sealed by rotary sizing.

The slide bearings of the examples and comparative examples were incorporated into the motors, and the oil film formation rate was measured by measuring the amount of energization between the shaft and the slide bearings while rotating each motor. Specifically, in a normal temperature (25 ° C.) environment, while rotating the motor at 2000 r / min, the shaft is held upright in the vertical direction and the shaft is swung between the vertical direction and the horizontal direction. The state of being allowed to be allowed to be rotated was alternately repeated every 2 seconds, and the oil film formation rate at this time was measured.

As shown in FIG. 13, in the motor using the slide bearing of the comparative example, the oil film formation rate is lowered at the time of swinging, and it can be seen that the shaft and the slide bearing are in contact with each other. On the other hand, as shown in FIG. 12, in the motor using the slide bearing of the embodiment, the oil film formation rate was always 100% in both the upright position and the rocking state. Therefore, it was confirmed that the load capacity can be improved and the contact between the shaft and the slide bearing can be prevented by using the slide bearing of the embodiment.

1 Fluid dynamic bearing device 2 Shaft member 8 Bearing sleeve (plain bearing)
8'Pressure powder 11 Iron particles 12 Oxide coating 13a Opening 13b Internal pores 14 Molding lubricant A Radial bearing surfaces B, C Thrust bearing surfaces G1, G2 (Radial) Dynamic pressure groove G3 (Thrust) Dynamic pressure groove R1 , R2 Radial bearing T1, T2 Thrust bearing S Seal space

Claims (4)

It contains only iron powder as a metal powder, and consists of a green compact in which the particles are bonded to each other by an oxide film formed on the surface of the iron powder particles, and slides through a mating material to be supported and a lubricating film. In a plain bearing having a bearing surface
A dynamic groove made of a molded surface is provided on the bearing surface, and the bearing surface is provided with a dynamic pressure groove.
The density of the green compact is 6.7 g / cm ³ or more, and
The bearing surface has a large number of minute recesses whose communication with the internal pores is blocked by the oxide film.
A plain bearing having an oil content of 4 vol% or less and a surface opening ratio of the bearing surface of 40% or more. The plain bearing according to claim 1, wherein the oil permeability is 0.01 g / 10 min or less. The slide bearing according to claim 1 or 2 , and a shaft member as a mating material inserted in the inner circumference of the slide bearing are provided between the bearing surface of the slide bearing and the outer peripheral surface of the shaft member. A hydrodynamic bearing device that non-contactly supports the shaft member in a relative rotatable manner by the pressure of the lubricating film in the radial bearing gap. The fluid dynamic bearing device according to claim 3 , the rotor magnet provided on the rotating side of the slide bearing and the shaft member, and the stator provided on the fixed side of the slide bearing and the shaft member. Motor with coil.

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